3 files changed, 50 insertions, 5 deletions
diff --git a/src/2021/day5/aoc.cpp b/src/2021/day5/aoc.cpp
index 174882e..e9fc1ed 100644
--- a/src/2021/day5/aoc.cpp
+++ b/src/2021/day5/aoc.cpp
@@ -15,6 +15,16 @@ static void get_number(const char** pp, int* d) {
 }
 
 void fill(std::vector<int>& b1, std::vector<int>& b2, const line& l, int width) {
+  if (l.is_vertical() || l.is_horizontal()) {
+    l.traverse([&b1, &b2, width](line::point p) {
+      b1[p.y * width + p.x] += 1;
+      b2[p.y * width + p.x] += 1;
+    });
+  }
+
+  if (l.is_diagonal()) {
+    l.traverse([&b2, width](line::point p) { b2[p.y * width + p.x] += 1; });
+  }
 }
 
 std::pair<int, int> day5(line_view file) {
@@ -33,6 +43,9 @@ std::pair<int, int> day5(line_view file) {
       }
       p++;
     }
+    if (l.p2 < l.p1) {
+      std::swap(l.p1, l.p2);
+    }
     maxx = std::max(maxx, std::max(l.p1.x, l.p2.x));
     maxy = std::max(maxy, std::max(l.p1.y, l.p2.y));
     vs.push_back(l);
@@ -42,7 +55,7 @@ std::pair<int, int> day5(line_view file) {
   maxx += 1;
   maxy += 1;
 
-  printf("%d, %d\n", maxx, maxy);
+  // printf("%d, %d\n", maxx, maxy);
   std::vector<int> board1(maxx * maxy, 0);
   std::vector<int> board2(maxx * maxy, 0);
   for (auto& l : vs) {
diff --git a/src/2021/day5/aoc.h b/src/2021/day5/aoc.h
index c57f439..bd8c346 100644
--- a/src/2021/day5/aoc.h
+++ b/src/2021/day5/aoc.h
@@ -1,6 +1,7 @@
 #pragma once
 
 #include "common.h"
+#include <math.h>
 
 namespace aoc2021 {
 
@@ -8,9 +9,41 @@ struct line {
   struct point {
     int x;
     int y;
+
+    bool operator<(const point& p) const noexcept { return x < p.x ? true : x > p.x ? false : y < p.y; }
+    point move_h(int d) { return {x + d, y}; }
+    point move_v(int d) { return {x, y + d}; }
+    point move_p(int d) { return {x + d, y + d}; }
+    point move_d(int d) { return {x + d, y - d}; }
   };
   point p1;
   point p2;
+
+  bool is_vertical() const noexcept { return p1.x == p2.x; }
+  bool is_horizontal() const noexcept { return p1.y == p2.y; }
+  bool is_diagonal() const noexcept { return std::abs(p2.x - p1.x) == std::abs(p2.y - p1.y); }
+
+  template <typename F>
+  void traverse(F&& f) const noexcept {
+    auto next = [this](point x) {
+      if (is_vertical()) {
+        return x.move_v(1);
+      }
+      if (is_horizontal()) {
+        return x.move_h(1);
+      }
+      if (is_diagonal()) {
+        return p2.y > p1.y ? x.move_p(1) : x.move_d(1);
+      }
+      return x;
+    };
+    point p = p1;
+    while (p < p2) {
+      f(p);
+      p = next(p);
+    }
+    f(p); // p == p2
+  }
 };
 
 std::pair<int, int> day5(line_view);
diff --git a/test/test_2021.cpp b/test/test_2021.cpp
index 0096a8c..3208c4b 100644
--- a/test/test_2021.cpp
+++ b/test/test_2021.cpp
@@ -37,9 +37,8 @@ TEST_CASE("Giant Squid", "[2021]") {
 }
 
 TEST_CASE("Hydrothermal Venture", "[2021]") {
-  line_view lv = load_file("../src/2021/day5/input0");
+  line_view lv = load_file("../src/2021/day5/input");
   auto p = aoc2021::day5(lv);
-  // REQUIRE(5774 == p.first);
-  REQUIRE(5 == p.first);
-  REQUIRE(12 == p.second);
+  REQUIRE(5774 == p.first);
+  REQUIRE(18423 == p.second);
 }